The Arduino Yun Shield

A few years ago, the most common method to put an Arduino project on the web was to add a small router loaded up with OpenWrt, wire up a serial connection, and use this router as a bridge to the Internet. This odd arrangement was possibly because the existing Arduino Ethernet and WiFi shields were too expensive or not capable enough, but either way the Arduino crew took notice and released the Arduino Yun: an Arduino with an SoC running Linux with an Ethernet port. It’s pretty much the same thing as an Arduino wired up to a router, with the added bonus of having tons of libraries available.

Since the Yun is basically a SoC grafted onto an Arduino, we’re surprised we haven’t seen something like this before. It’s an Arduino shield that adds a Linux SoC, WiFi, Ethernet, and USB Host to any Arduino board from the Uno, to the Duemilanove and Mega. It is basically identical to the Arduino Yun, and like the Yun it’s completely open for anyone to remix, share, and reuse.

The Yun shield found on the Dragino website features a small SoC running OpenWrt, separated from the rest of the Arduino board with a serial connection. The Linux side of the stack features a 400MHz AR9331 (the same processor as the Yun), 16 MB of Flash, and 64 MB of RAM for running a built-in web server and sending all the sensor data an Arduino can gather up to the cloud (Yun, by the way, means cloud).

About the only reason I can think of for the Arduino-ness in any pairing of an Atmel with an Arm, would be to use the ability of the Atmel chip to sleep in low power mode, and wake up the ARM board Yun or Pi, at regular intervals to do the real work. Both the SOC in the Yun and the Broadcom SOC on the Pi are infinitely more capable than the Atmel chip (at the expense of significantly higher power consumption).

For battery powered projects, I can see some scenarios where this might be a solution, but equally, I suspect the SOCs may already have some sort of sleep capability, given their target market.

I suppose the die hard Adruino fans might also argue that you can use all of the arduino libraries in your project, but that’s a bit like saying I keep my ZX81 hanging off the back of my gaming rig, because it allows me to use my 64K ram pack.

Others are free to disagree of course.. can anybody think of a problem, to which a Yun or Yun-clone (Yum perhaps?) is the best solution?

I think the yun and similar were born to take the market segment of the people using routers to connect to the internet.
I have explained here why it is great to use a router to connect to the internet: http://www.electrobob.com/web-interfaces/

In summary, it is about getting your project online that about processing power. It also goes down to cost as well: a bare wifi module costs the same or more compared to a router but has a lot of things lacking.

The Yùn is not only the AR9331 WiSoC, a Flash SPI and a DRAM chip + Leonardo’s ATmega32U4, it also contains an important feature that this board is missing: an USB hub and a microSD card combo. This is very important for the USB stability issue, see https://forum.openwrt.org/viewtopic.php?id=39956 for details.

The wart to the standard Arduino form factor will make it incompatible with Mega boards as it will cover some I/Os.

Thanks for that info on the USB issue, but note that that forum discussion is marked “[SOLVED]”. If you look near the end of the thread you see them discussing a patch which helps (fixes?) this problem:https://dev.openwrt.org/changeset/39212

This shield is great for people not using arduino as an alternative to buying a router.
Still, there are some things I wonder about it: is the wifi calibrated? Why, if the AR9331 supports dual antennas there is not one already integrated on the PCB? Why did they not break out on some port other pins from the AR9331 except serial and spi ?

Why not dual antennas? Cost, size, power consumption and expense. That, and this thing isn’t designed to be a dual-stream WiFi router, there are already hundreds of those. This is a device that leverages the economies of scale from market of cheap WiFi routers to allow people to bring wifi connectivity and a web front-end to Arduino / MCU applications.

I meant PCB antenna which is a circuit trace made on the board. I would think it would be cheaper to have that than a second PCB and a dangling wire, but anyone knowing the design cost can prove me wrong.

Seems like a cheaper smaller VAX with WiFi. Or a soup dumpling, only with a CPU and WiFi.

Not particularly useful comparisons though, are they?

This is superficially like the sparkcore in that it combines wifi and an MCU. It is different though in that you bring your own MCU for this one, also, the WiFI SoC runs linux, and has way more memory than the sparkcore. There are other major differences, but that is a good start.

that 10W includes the 2.5W for the usb host + you get more power and memory.
Still, thinking about what that router/yun can do with 0.5W is quit amazing. A typical router with AR9331 can be 1W from the mains (assuming just wifi connection)

Those chips that are used in tablets should have some power control, but I don’t know how that is available in the pcduino. maybe there it runs at 100% all time?

The thing that the Yun has that the normal Wifi modules don’t is access point mode. If you want to make something like a AR Drone style quad copter this is great solution. Having to setup an AD-Hoc network sucks. Plus the Arduino can handle all the real time stuff and ANALOG while the Yun servers up the WIFI and DHCP.